To adjust and change the contour of a vehicle seat, the air cushions available in the vehicle seat are selectively filled with air end emptied. To do this, so-called cross rocker switches with four switching positions, upwards-downwards and forwards-backwards are used. In the upwards-downwards switching position, the form (i.e. the contour or total air quantity inside the air cushion) should remain constant and merely vertically adjust the curvature of the air cushion or lordosis position. In the frontwards-backwards switching position, the form or intensity of the lordosis adjustment to the current position can be strengthened or weakened, in other words, the curvature of the lordosis can be changed.
To achieve vertical adjustment, the pressures in the air cushion are regulated in such a way that certain pressure values are set in the individual air cushions for each adjusting position. To do this, it is customary for pressure sensors to measure the pressures and report them back to a pump control or separate control valve. To measure the pressure—to be more precise, the excess pressure in one or several air cushions—two absolute sensors are used, i.e. sensors designed to measure absolute pressure. In this case, one sensor measures the absolute pressure of the air cushion and the other sensor the absolute pressure of the surroundings. The excess pressure in the air cushion is determined with an electronic unit from the difference of the absolute pressures mentioned above. The disadvantage of this is that two absolute sensors are necessary and this increases the cost of materials and assembly effort for the kind of arrangement being described here, thus impacting manufacturing costs. Another method measures the excess pressure prevailing in an air cushion directly with the help of a relative pressure sensor. Such a sensor must have a separate air channel connected to the surroundings, but owing to this constructive peculiarity, it is relatively expensive. Therefore, the manufacturing costs of the second method are virtually no different from those of the first.
In vehicle seats that have merely two air cushions and no pressure sensor, the form increase usually takes place by filing both air cushions simultaneously without taking the position adjusted so far into account. Even an adjustment in vertical direction takes place irrespective of the adjusted position by filling the air cushion lying in adjustment direction and emptying the air cushion facing away from the adjustment direction.
The disadvantage of the known state-of-the-art devices and methods for adjusting a vehicle seat contour is that measuring the pressures merely allows one to evaluate the force exerted. The actual adjustment position is assumed here to be given as direct correlation. Moreover, the utilization of pressure sensors entails significant additional manufacturing costs and more assembly effort. However, if pressure sensors are dispensed with, then the contour of the vehicle seat can no longer be selectively adjusted.